Turbulence Characteristics Study of the Emulsified Flow

SIEW FAN WONG

School of Energy and Chemical Engineering

Xiamen University Malaysia

Selangor, 43900

MALAYSIA

siewfan.wong@xmu.edu.my

SHARUL SHAM DOL

Department of Mechanical Engineering

Abu Dhabi University

Abu Dhabi, P.O. Box 59911

UNITED ARAB EMIRATES

sharulshambin.dol@adu.ac.ae

Abstract: - The presence of emulsions brings numerous undesirable effects to the oil and gas industry; it affects

the flow regimes and flow behavior in the pipeline, reduces the quality of crude oil, requires longer retention time

in the separation vessels, causes corrosion to the transport system, contaminates catalyst used in the refining

process that leads to huge economic losses. The formation of emulsions; dynamic break-up and coalescence of

the dispersed droplets tend to diminish the turbulence in the flow. This suggests that turbulence is consumed

during the emulsification process. The turbulence characteristics of the water-oil emulsions flow in the pipeline

are examined and discussed. The Reynolds stress and turbulence intensity analysis show that turbulence activities

and transport influence the formation of emulsions and it is induced from the constriction of pipeline. The largest

amount of fluctuating components are observed nearest to the constriction and the turbulence is diminishing as

the flow flows further away from the constriction. This research work enables the oil industry to provide a better

strategy in treating the emulsification phenomena in the pipeline transportation system.

Key-Words: - constrictions, crude oil, emulsions, Reynolds stress, turbulent intensity, UVP, water cuts

1 Introduction In the oil and gas industry, emulsification in the

pipeline flow is unavoidable as crude oil usually

comes together with water from the reservoir. Crude

oil must pass through different processes before it is

processed and refined into more useful products such

as gasoline, petroleum, liquefied petroleum gas,

lubricating oil, asphalt, paraffin wax, diesel fuel and

bitumen. Throughout all these processes, the

agitation, mixing as well as the turbulence energy

formed through downhole wellbores, surface chokes,

valves, pumps, and pipes will directly lead to the

formation of emulsion in the crude oil flow [1].

The formation of emulsions is undesirable in the

oil and gas industry because emulsification brings a

number of problems; it affects the flow regimes and

flow behaviour, reduces the crude oil’s quality,

occupies a volume in the pipeline, reduces the mass

flow rate, requires longer retention time in the

separation vessels, causes corrosion to the transport

system, contaminates catalyst used in the refining

process and increases operating cost. It has been

discovered that the presence of emulsions also can

affect the friction factor of the flow, as well as the

viscosity of the mixture and pressure drop along the

pipeline [2-4].

Wong et al. [5] carried out a study on the

characteristics of the water-in-oil (W/O) emulsions in

order to develop a better understanding on the W/O

emulsions. Three parameters, namely, water cuts

(WC), Reynolds number and pipeline constrictions

were studied. The study on the stability of W/O

emulsions of different controlling parameters shows

that, with the increase in the water cuts, the stability

of the emulsions is increased and with the increase in

the Reynolds number, the stability of emulsions is

increased. From the study of the stability of W/O

emulsions, it is concluded that the stability of the

emulsions increases with the increase in the water

cuts and Reynolds number.

Dol et al. [6] did an experimental study on the

effects of W/O emulsions in the pipeline flow to

understand the emulsions formation mechanically

and to discover the effects of water-in-oil emulsions

to the pipeline flow transport by relating the effect of

emulsions to the wall shear stress or friction of the

pipe. From this study, it is recommended the crude

oil be delivered at a higher Reynolds number. Lower

wall shear stress is desirable because lower wall shear

WSEAS TRANSACTIONS on HEAT and MASS TRANSFER Siew Fan Wong, Sharul Sham Dol

E-ISSN: 2224-3461 45 Volume 14, 2019

stress indicates lower friction in the flow and

therefore pressure drop in the flow can be reduced.

This helps in minimizing the energy losses during the

transportation of crude in the pipeline.

With reference to these findings, it is known that

the emulsified flow or formation of emulsions in the

pipeline is closely related to turbulence. However,

the roles of turbulent flow generated in the pipeline

in emulsification process has not yet been

understood. Hence, further investigation and

additional analysis are needed to confirm the

turbulence activities in the emulsified pipeline flow.

Therefore, this paper will discuss the turbulence

characteristics of the water-oil emulsions flow in

order to have a better understanding on the roles of

turbulence in the formation of emulsion in the

pipeline flow. The turbulence characteristics of the

water-oil emulsions flow in the pipeline are

examined and discussed through the analysis of

Reynolds stress and turbulence intensity of the flow

field. This will then broadly contribute to the

transportation of crude, i.e. with less emulsions

formation, as the energy for the formation of

emulsions can be controlled accordingly with the

understanding on the roles of turbulence activities in

the emulsification process.

This study investigates the influence of the water

cuts (WC) ranging from 0 to 40%, transitional (2400

< Re < 2800) flow regime as well as pipeline

constrictions with types of gradual contraction with a

contraction ratio of 0.50 (GC 0.50), gradual

contraction with a contraction ratio of 0.75 (GC

0.75), sudden contraction with a contraction ratio of

0.50 (SC 0.50) and sudden contraction with a

contraction ratio of 0.75 (SC 0.75), to the pipeline

flow transport by using a continuous flow loop.

2 Methodology

2.1 Crude oil The primary material used in this study was Miri

Light Crude (MLC), provided by PETRONAS Miri

Crude Oil Terminal (MCOT). This type of crude oil

is defined as light crude stock as it has an API gravity

of 29.79o. The properties of MLC are as follow: the

density at 15℃ is 0.8768 g/cm3, the kinematic

viscosity at 25℃ is 4.785 cSt, the asphaltenes content

is 0.43 wt% and the BS&W is 0.05 vol%.

The next material used in this study was filtered

water. Filtered water was obtained by filtering the tap

water from local municipal water supply. The

purpose of using filtered water is to remove the

unwanted rust and sediment particles present in the

tap water.

2.2 Experimental set-up The experimental flow rig made for the use of this

study is presented in Fig. 1. The flow rig is a closed-

circuit loop which consists of a 55 liters storage tank,

a positive displacement pump, a digital flow meter, a

pressure measurement device, and two 90° bend

pipeline constrictions. The 90° bend pipeline

constriction is served to replicate the usage of choke

valves in the oil and gas industry, which causes the

formation of emulsions. The flow rig is constructed

using the 2” stainless-steel (SS) pipes with an inner

diameter of 48 mm and a wall thickness of 2 mm. The

test segment AB is made of plexiglass with an inner

diameter of 44 mm and wall thickness of 1 mm.

Fig. 1. Actual photo of the flow rig.

2.3 Velocity measurement In this study, velocity profile of the flowing fluid

in the pipeline is captured by using UVP (ultrasonic

velocity profiler). The working principle of UVP

system is it uses pulsed ultrasonic Doppler Effect

together with the echography relationship [6]. The

ultrasonic (US) transducer transmits short US pulses

into the flowing fluid and when the pulses hit on the

minuscule particles in the flowing fluid, it will reflect

to the transducer. From there, the system processes

the data into velocity information.

Fig. 2. Schematic diagram of the experimental setup

for velocity measurement.

WSEAS TRANSACTIONS on HEAT and MASS TRANSFER Siew Fan Wong, Sharul Sham Dol

E-ISSN: 2224-3461 46 Volume 14, 2019

To carry out the experiments, the US transducer

was placed on the transducer holder with an

incidence angle of 10° at the measurement location,

starting from measurement location 13 x/D to 63 x/D

(as shown in Fig. 2). To obtain the streamwise

velocity gradient (𝜕𝑈

𝜕𝑋), the velocity of the flowing

fluid was measured across the direction y, which is

perpendicular to the direction of the flowing fluid in

the pipeline (direction x).

2.4 Reynolds stress

Reynolds stress is one of the important

characteristics in the study of turbulence activities. It

is the shear generated in the fluctuating component of

the flow and as has been known, shear is one of the

important sources in producing turbulence. With

reference to the Turbulent Kinetic Energy Budget,

the Reynolds stress (𝑢𝑖𝑢𝑗) term appears at the “loss

to turbulence” term of mean kinetic energy equation

and shear production term of turbulent kinetic energy

equation. This shows the significant contribution of

Reynolds stress to the transfer and production of

turbulent energy in the flow. The Reynolds stress

analysis in this study will bring to an understanding

on the transport of momentum due to the velocity

fluctuation in the flow as a result of the pipeline

constriction effect and also the W/O emulsions

effects. The Reynolds stress in this study is presented

in its normalized form. It is normalized by the

averaged streamwise velocity of the flow, giving the

normalized Reynolds stress - the 𝑢′𝑢′

𝑈2 .

2.5 Turbulent intensity

Turbulence intensity analysis is used for the study

of the turbulence characteristics of emulsified flow

because it is a measure used for characterizing the

turbulence level in term of percentage. In other

words, turbulence intensity allows one to examine the

turbulence level in the flow statistically. In this study,

turbulence intensity is used to examine the

fluctuations of the streamwise velocity component. A

larger turbulence intensity indicates a higher

turbulence level and vice versa. In the present work,

the turbulence intensity is calculated using

Turbulence intensity U

u'

(1)

where 𝑢′ stands for root-mean-square of turbulent

velocity fluctuation and �̅� stands for the averaged

streamwise mean velocity.

In this section, the turbulence intensity along the

pipeline (increase in the pipe length) after the

pipeline constriction and the turbulence intensity

with respect to different water cuts are compared and

discussed. The purpose is to understand the

correlation in between the turbulence level of the

flow with the emulsification behaviour as well as to

confirm the proclamation made in the previous

findings of [6] – an increase in water cuts leads to

drag-reduction effect as a result of turbulence

diminishing by the presence of emulsions, thereby

resulted in the decrease of wall shear stress, τw.

3 Results and Discussions

3.1 Reynolds stress comparisons along the

pipeline Figure 3 (a) and (b) to Fig. 7 (a) and (b) present

the normalized Reynolds stress (𝑢′𝑢′

𝑈2 ) from the

pipeline constriction type GC 0.50 at the pipeline

location of 13 x/D and 63 x/D respectively, for 0 to

40% WC. The 𝑢′𝑢′

𝑈2 profiles for pipeline constrictions

of GC 0.75, SC 0.50 and SC 0.75 show about the

same profiles.

From these figures, it is determined that the 𝑢′𝑢′

𝑈2

peak region at the location 13 x/D downstream the

pipeline constriction is larger than that at 63 x/D. As

shown in Fig. 3 (a) to Fig. 7 (a), the 𝑢′𝑢′

𝑈2 peak region

for 0%, 10%, 20%, 30% and 40% WC covers about

0.35, 0.20, 0.45, 0.40 and 0.25 of the pipe radius (y/R)

at the pipeline location of 13 x/D. As the fluid flows

further downstream to location 63 x/D of the pipeline

(increase in the pipe length), the results show that the 𝑢′𝑢′

𝑈2 peak region for 0 %, 10%, 20%, 30% and 40%

WC reduces to 0.25, 0.15, 0.30, 0.10 and 0.10 y/R,

respectively (as shown in Fig. 3 (b) to Fig. 7 (b)). This

indicates that nearest to the pipeline constriction, the

transport of momentum in the pipe that governs by

the fluctuating components cover a larger cross-

sectional area of the pipe since the 𝑢′𝑢′

𝑈2 peak region is

larger. Further downstream the pipeline, the

fluctuating components governs a smaller cross-

sectional area of the pipe governs for the momentum

transport. Only the flow near to the pipeline wall (y/R

= 0) shows a significant momentum transport by the

fluctuating component. This indicates that further

downstream, the transport of flow is mostly governed

by the main flow. With reference to these

observations, it is understood that the fluctuating

components are most energetic at the location nearest

to the constriction of the pipeline (13 x/D) and

weaken with the increase in the pipe length. This

WSEAS TRANSACTIONS on HEAT and MASS TRANSFER Siew Fan Wong, Sharul Sham Dol

E-ISSN: 2224-3461 47 Volume 14, 2019

suggests that the pipeline constriction is the source of

turbulence production, where the largest amount of

fluctuating components are observed there.

Fig. 3. The 2/'' Uuu profile at location (a) 13 x/D

and (b) 63 x/D for pure crude after the pipeline

constriction type GC 0.50.

Fig. 4. The 2/'' Uuu profile at location (a) 13 x/D

and (b) 63 x/D for 10% WC after the pipeline

constriction type GC 0.50.

Fig. 5. The 2/'' Uuu profile at location (a) 13 x/D

and (b) 63 x/D for 20% WC after the pipeline

constriction type GC 0.50.

Fig. 6. The 2/'' Uuu profile at location (a) 13 x/D

and (b) 63 x/D for 30% WC after the pipeline

constriction type GC 0.50.

Fig. 7. The 2/'' Uuu profile at location (a) 13 x/D

and (b) 63 x/D for 40% WC after the pipeline

constriction type GC 0.50.

The 𝑢′𝑢′

𝑈2 results also show that as the water cuts

increases, the momentum transfer due to velocity

fluctuation components is reduced. Likewise, the

fluctuating components become less energetic as the

water cuts increases. It has been extensively reported

that turbulence suppression is one of the main factors

that leads to the decrease in Reynolds stress [7 and

8]. Lower Reynolds stress indicates that there is less

momentum transfer. This is because fluctuating

velocity components in the turbulent flow induces

lesser kinetic energy. Since the results show that the 𝑢′𝑢′

𝑈2 decreases with the increase in water cuts, it is

logical to suggest that the presence of emulsions is

able to suppress the velocity fluctuation in the flow.

Since turbulence is due to the fluctuation of the

velocity component in the flow and emulsions are

capable of suppressing the fluctuation, therefore

increase in the water cuts (increase in emulsions) will

directly lead to the diminishing of turbulence.

3.2 Turbulent intensity comparisons along the

pipeline Figure 8 (a) and (b) to Fig. 15 (a) and (b) present

the distribution of streamwise turbulence intensity

(𝑢′

�̅�) from the pipeline constriction type GC 0.50 at

pipeline location of 13 x/D and 63 x/D, for 0 to 40%

WC respectively. The streamwise 𝑢′

�̅� profiles for

pipeline constrictions of GC 0.75, SC 0.50 and SC

0.75 show similar profiles.

From Fig. 8 to Fig. 15, it is observed that the

streamwise 𝑢′

�̅� peak region (fluctuation region) at

pipeline location 13 x/D downstream the constriction

is larger than that at the 63 x/D downstream

constriction. For pure crude, it is determined that the

streamwise 𝑢′

�̅� peak region reduces from 0.35 to 0.25

of the pipe radius (y/R) as the flow flows from 13 x/D

to 63 x/D. For emulsified flow with 10%, 15%, 20%,

25%, 30%, 35% and 40% WC, the results show that

the 𝑢′

�̅� peak region reduces from 0.20 to 0.15 y/R, 0.35

WSEAS TRANSACTIONS on HEAT and MASS TRANSFER Siew Fan Wong, Sharul Sham Dol

E-ISSN: 2224-3461 48 Volume 14, 2019

to 0.25 y/R, 0.40 to 0.25 y/R, 0.40 to 0.10 y/R, 0.40 to

0.10 y/R, 0.40 to 0.05 y/R and 0.30 to 0.10 y/R,

respectively.

Fig. 8. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 0% WC after the pipeline constriction

type GC 0.50.

Fig. 9. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 10% WC after the pipeline

constriction type GC 0.50.

Fig. 10. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 15% WC after the pipeline

constriction type GC 0.50.

Fig. 11. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 20% WC after the pipeline

constriction type GC 0.50.

Fig. 12. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 25% WC after the pipeline

constriction type GC 0.50.

Fig. 13. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 30% WC after the pipeline

constriction type GC 0.50.

Fig. 14. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 35% WC after the pipeline

constriction type GC 0.50.

Fig. 15. Streamwise Uu /' distribution at (a) 13 x/D

(b) 63 x/D for 40% WC after the pipeline

constriction type GC 0.50.

The reduction in the streamwise 𝑢′

�̅� fluctuation

region as the flow flows further downstream

indicates that the turbulence in the flow is

WSEAS TRANSACTIONS on HEAT and MASS TRANSFER Siew Fan Wong, Sharul Sham Dol

E-ISSN: 2224-3461 49 Volume 14, 2019

diminished. Since the damping of streamwise 𝑢′

�̅� is

observed in both the pure crude and emulsified flow,

the result in this section is unable to prove that

turbulence in the flow is consumed for the formation

of emulsions. However, the results do suggest that

turbulence is induced at the constriction of the

pipeline. This is because the results show that the

streamwise 𝑢′

�̅� fluctuation region is larger at 13 x/D,

where this location is the nearest to the constriction

of the pipeline.

The results also show that the maximum

streamwise turbulence intensity decreases with the

increase in the water cuts from 0% to 40%. With the

increase in water cuts from 0% to 40%, the maximum

streamwise turbulence intensity decreases from

100% to about 25% only. The decrease in the

maximum streamwise turbulence intensities with the

increase in water cuts indicates that the turbulence

level in the flow with higher water cuts is lower. This

is because at higher water cuts, the amounts of

emulsions formed are higher as well. As a result of

that, the frequency of emulsion-emulsion collision is

increased due to the increase in the compactness of

the emulsions in the flow.

This is supported by [9] whose report has stated

that the intensive exchange of momentum between

the particles during the particle-particle collisions

will lead to the proximity of their velocities, resulting

in the decrease of the velocity fluctuation. This

means that an increase in the water cuts (amount of

emulsions) will lead to the decrease in the velocity

fluctuation owing to more exchange of momentum

between the emulsions. Thus, the turbulence level in

the flow reduces with the increase in the input of

water cuts, as presented by the results shown here.

The results suggest that the presence of emulsions

diminishes the turbulence in the flow. As a result of

diminishing in turbulence, drag in the flow is

reduced, leading to a drag the reduction effect with

the increase in the water cuts. This has confirmed the

discussion in [6] that the drag reduction phenomenon

is caused by the diminishing in turbulence due to the

presence of emulsions.

5 Conclusion In order to confirm the postulation made in the

previous findings that turbulence is diminished with

the increase in the water cuts (increase in the amount

of emulsions), this chapter has investigated the

turbulence characteristics statistically. The

normalized Reynolds stress (𝑢′𝑢′

𝑈2 ) and the streamwise

turbulence intensity (𝑢′

�̅�) are analyzed. The results

presented here provide an insight into the roles or

contribution of turbulence in the emulsification

process. Through the examination on the 𝑢′𝑢′

𝑈2 and 𝑢′

�̅�,

it has been demonstrated that the turbulence is the

source for the formation of emulsions and turbulence

is induced from the constriction of pipeline.

References:

[1] Lim, J.S., S.F. Wong, M.C. Law, Y. Samyudia,

and S.S. Dol, A Review on the Effects of Emulsions

on Flow Behaviours and Common Factors Affecting

the Stability of Emulsions. Journal of Applied

Sciences, 15, 2015, pp. 167-172.

[2] Dol, S.S., Chan, M.S., Wong, S.F. and Lim, J.S.,

Experimental Study on the Effects of Water-in-Oil

Emulsions to the Ρressure Drop in Ρipeline Flow,

International Journal of Chemical and Molecular

Engineering, 10, 2016, pp. 1528-1535.

[3] Dol, S.S. and Lim, J.S., The Effect of Flow-

Induced Oil-Water Emulsions on Pressure Drop.

International Journal of Theoretical and Applied

Mechanics, 2, 2017, pp. 73-78.

[4] Dol, S.S. and Lim, J.S., The Effect of Dissipation

Energy on Pressure Drop in Flow-induced Oil-water

Emulsions Pipeline, WSEAS Transactions on

Environment and Development, 14, 2018, pp. 182-

189.

[5] Wong, S.F., Dol, S.S., Wee, S.K. and Chua, H.B.,

Miri Light Crude Water-in-oil Emulsions

Characterization–Rheological Behaviour, Stability

and Amount of Emulsions Formed, Journal of

Petroleum Science and Engineering, 165, 2018, pp.

58-66.

[6] Dol, S. S.; Wong, S. F.; Wee, S. K.; Lim, J. S.,

Experimental Study on the Effects of Water-in-oil

Emulsions to Wall Shear Stress in the Pipeline Flow,

Journal of Applied Fluid Mechanics, Vol. 11 Issue 5,

2018, pp. 1309-1319.

[7] Li, F.-C., B. Yu, J.-J. Wei, and Y. Kawaguchi,

Turbulent drag reduction by surfactant additives,

John Wiley & Sons, 2012.

[8] Li, F.-C., Y. Kawaguchi, and K. Hishida,

Investigation on the characteristics of turbulence

transport for momentum and heat in a drag-reducing

surfactant solution flow, Physics of Fluids, 16(9),

2004, pp. 3281-3295.

[9] Varaksin, A.Y., Y.V. Polezhaev, and A.F.

Polyakov, Effect of Particle Concentration on

Fluctuating Velocity of the Disperse Phase for

Turbulent Pipe Flow, International journal of heat

and fluid flow, 21(5), 2000, pp. 562-567.

WSEAS TRANSACTIONS on HEAT and MASS TRANSFER Siew Fan Wong, Sharul Sham Dol

E-ISSN: 2224-3461 50 Volume 14, 2019